Glycol Dehydration Systems

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Dr. S. M. Anisuzzama Anisuzzaman n Lecturer Safety, Environmental Impact & Risk Management (KOG !"#$ Master of Engineering (Oil & Gas$ %niversiti %niversiti Malaysia Malaysia Saa'

GAS AND A ND GLYCOL GLYCOL DEHYDRA DEHYDR ATION SYSTEMS

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TABLE OF CONTENTS CHAPTER 1 INTRODUCTION

1.0 1.1

1.2

General Overview ................................................ .................................................. ............... C1-1 Petinent Legislation and Regulatory Requirements....................................... ....................... C1-2 1.1.1 Environmenta Environmenta Quality Quality Act, 1974 ............................................... ............................... C1-2 1.1.2 Occupational Occupational Safety and Health Health Act, 1994 1994 ................................................ ............... C1-2 1.1.3 Factories and Machineries Machineries Act, 1967. 1967. ................................................ ....................... C1-2 Glycol Dehydration Systems ....................................... .................................................. ....... C1-3 1.2.1 Types of Glycol .............................................. .................................................. ....... C1-3 1.2.2 Components Components of Dehydration Dehydration Systems....................................... ............................... C1-5 1.2.2.1 Glycol Contractor (Absorption (Absorption Column) .................................................. ............... C1-6 1.2.2.2 Flash Drum Drum ....................................................................................... ....................... C1-7 1.2.2.3 Glycol Regeneration Unit ................................ .................................................. ....... C1-7 1.2.2.4 Reboiler ............................................ .................................................. ....................... C1-7 1.2.2.5 Condenser…………………………………………………………………………..C1-8 1.2.2.6 Reflux Drum………………………………………………………… Drum……………………………………………………………………….C1-8 …………….C1-8

CHAPTER 2 SAFETY ISSUES AND CHALLEGES

2.1

BTEX Emission ........................................... .................................................. ....................... C2-9

CHAPTER 3 SAFETY AND HEALTH MANAGEMENT

3.1 3.2

3.3

Introduction.................................................. .................................................. ..................... C3-10 Risk Assessment Management Process ......................................... ..................................... C3-10 3.2.1 Hazards Identification ................................................ ............................................. C3-11 3.2.2 Risk Analysis ........................................... .................................................. ............. C3-12 3.2.2.1 Consequence. ............................................................................. ............................. C3-12 3.2.2.2 Frequency. Frequency. ................................................ .................................................. ............. C3-12 3.2.2.3 Risk Ranking............................................ .................................................. ............. C3-14 3.2.3 Risk Mitigating Mitigating / Risk Risk Control Control .......................................... ..................................... C3-15 Glycol Dehydration Systems Risk Assessment ............................................. ..................... C3-16 3.3.1 Identified Hazards ............................................ .................................................. ..... C3-16 3.3.2.1 Toxic Gasses Release to Atmosphere. Atmosphere. ............................................................... ..... C3-16 C3-16 3.3.2.2 Contacted with TEG. ....................................... .................................................. ..... C3-16 3.3.2.3 Fire or Explosion Due to Ignition of TEG. ............................................................. C3-17 C3-17 3.3.2.4 TEG Spill / Leak . ...................................................................................... ............. C3-17

CHAPTER 4 MITIGATION AND RECOMMENDATION

4.1

Mitigation and Recommendation Recommendation ........................................... ............................................. C4-19

CHAPTER 5 CASE STUDY

5.1

TEG Fire at Gas Dehydration Unit ................................................ ..................................... C5-20 5.1.1 Incident Information ................................................ ............................................... C5-20 5.1.2 Incident Detail .................................................. .................................................. ..... C5-20 5.1.3 Incident Root Cause ......................................... .................................................. ..... C5-20 5.1.3 Corrective Action and and Recommendation Recommendation ........................................... ..................... C5-21

GAS AND GLYCOL D EHYDRATION SYSTEM

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INTRODUCTION

General Overview

This assignment title ‘Gas and Glycol De hydration System’ were prepared, presented and submitted by the writer as a University’s requirement for course subject Safety, Environmental Impact & Risk Management (KOG11303) of Master of Engineering (Oil & Gas) programme.

Firstly, safety is defined as ‘the prevention of accidents through the use of appropriate technologies to identify the hazards of particular act ivities to be carried out or equipment/ instrumentation and eliminate or control the i dentified hazards before an accident occurs’.

Natural gases are found beneath the earth that was formed through the process of organic’s ‘cooking’ (organic theory) underneath the earth millions years ago and become a valuable resources to the nation’s economy such as Malaysia. Productions of natural gases are complex due to its properties that need several refining process so that it can be legally utilised by the consumer or industry since a water content shall be indicated in the agreement contract between supplier and buyer.

Gas dehydration system is one of the initial processes that shall be carried out before it can be transported, refined and utilised. The system is a technology of plant that created or inverted to separate gases from water vapour. Gas dehydration system is a system or unit to remove water content that mixed with the natural gases and normally this operation is carried out in the upstream stage of oil and gas.

There are several technics to remove water from gases that which by (1) absorption, using the liquid desiccants, (2) absorption, using solid desiccants and (3) cooling/ condensation below the dew point.

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1.1

Pertinent Legislation and Regulation Requirements

1.1.1

Environmental Quality Act, 1974

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The Environmental Quality Act (EQA), 1974 [Act 127] (Incorporating latest amendment – Act A1441/2012) is “an Act relating to the prevention, abatement, control of pollution and enhancement of the environment, and for purposes connected therewith”. EQA 1974 forms the main frame for the environmental legal requirements in Malaysia which cover matters enumerated within the Federal List of the Constitution.

1.1.2

Occupational Safety and Health Act, 1994

The Occupational Safety and Health Act (OSHA), 1994 [ Act 514] ( Incorporating all st

amendments up to 1 January 2006 ) is “an Act to make further provisions for securing

the safety, health and welfare of persons at work, for protecting others against risks to safety or health in connection with the activities of person at work, to establish the National Council for Occupational Safety and Health, and for matters connected therewith”. OSHA 1994 applies throughout Malaysia to the industries as specified in the First & Third Schedules.

The Act provides a framework for self-regulations to ensure safety and health at work lies with those who create the risks and those who work with the risks, by emphasising on the prevention of accidents, ill health and injury. The Act supersedes and is complementary to any other written law relating occupational safety and health. Salient provisions of the Act include the establishment of a Safety Policy, Safety and Health Committee, employment of a competent safety officer, and the notification of accidents, dangerous occurrence, occupational poisoning and occupational diseases to the Department of Safety and Health (DOSH).

1.1.3

Factories and Machinery Act, 1967

The Factories and Machinery Act (FMA), 1967 [ Act 139] ( Incorporating all amendments st

up to 1 January 2006 ) is “an act to provide for control of factories with respect to R B Kennedy Enis



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matters relating to the safety, health and welfare of person therein, the registration and inspection of machinery and for matters connected therewith”. FMA 1967 provides a framework for the control of factories and machinery, through the supervision of the Inspectors by the powers provisioned to them by the Act, with respect to matters relating to the safety, health and welfare of persons, and the registration and inspection of the machinery.

1.2

Glycol Dehydration Systems

Glycol Dehydration Systems is the most commonly used in oil and gas industry (which is up to 90%) to remove water vapour from natural gas. Natural gas must be dehydrated (remove water vapour) to prevent hydrates formation (an icy solid-formed of due to combination of 10% hydrocarbon and 90% water vapour) that could lead to plugging/ blocking of pipe’s function, to prevent corrosion of metal (degradation of metal due to exposing with water vapour) and requirements of downstream processing (water may react with same catalyst in downstream processing).

1.2.1

Types of Glycol

Glycol is a chemical substance used in Glycol Dehydration Systems because of its properties of having lower vapour pressure and does not evaporated into the vapour phase. It is also less soluble in liquid hydrocarbons than methanol. Glycol is economically because of it could be recovered and reused for the treatment, reduces the operating costs as compared to the others che mical substances.

There are three types of glycols used: ethylene glycol (EG), diethylene glycol (DEG) and triethelyne (TEG) (see Table 1.2-1 for its physical properties). The following specific applications are recommended:-

a. For natural gas transmission lines, where hydrate protection is of importance, EG is the best choice (see Figure 1.2-1 ). It provides the highest hydrate depression, although this will be at the expense of its recovery of its high vapour pressure.

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b. EG is used to protect vessels or equipment handling hydrocarbon compounds, because of its low solubility in multicomponent hydrocarbons (see Figure 1.2-2 ).

c. For situations were vaporization losses are appreciable, DEG or TEG should be used, because of their lower vapour pressure (see Figure 1.2-3 ).

Figure 1.2-1: Chemical compositions of ethylene glycol (EG)

Figure 1.2-2: Chemical compositions dithylene glycol (DEG)

Figure 1.2-3: Chemical compositions of triethelyne glycol (TEG) R B Kennedy Enis

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It is of importance to mention that when hydrate inhibitors in general are injected in gas flow lines or gas gathering networks, installation of high-pressure free-water knockout at the wellhead is of value in the operation. Removing of the free water from the gas stream ahead of the injection point will cause a significant savings in the amount of the inhibitor used.

Table 1.2-1: Physical Properties of EG, DEG and TEG

1.2.2

Components of Glycol Dehydration Systems

Glycol Dehydration System is the most common solvent used in dehydration unit in oil and gas industry due to its economic as shown in Figure 1.2-4 and Figure 1.2-5 . The systems act as an absorber of water vapour in natural gas i.e. absorption, which is defines as the transfer of a component from the gas phase to liquid phase, is more favourable at a lower temperature and higher pressure .

Figure 1.2-4: Glycol Dehydration Systems R B Kennedy Enis



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1.2.2.1 Glycol Contractor (Absorption Column)

The wet natural gas enters the absorption column near its bottom and flows upward through the bottom tray to the top tray and out at the top of column. Usually six to eight trays are used. Lean (dry) glycol is fed at the top of the column and it flows down from tray to tray, absorbing water vapour from the natural gas. The rich (wet) glycol leaves from the bottom of the column to the glycol regeneration unit. The dry natural gas passes through mist mesh to the sales line (see Figure 1.2-6 for water dew point with concentration of TEG).

Figure 1.2-5: Schematic of Glycol Dehydration Systems

Figure 1.2-6: Water Dew Point with Various Concentration of TEG

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1.2.2.2 Flash Drum

The wet glycol leaves the bottom of the absorber, flows through a pressure control valve, (Pressure Let-down valve, PLV) then into a flash drum. In the flash drum the wet glycol pressure is reduced to enable light hydrocarbons, mainly methane to escape from the solution (Glycol, water and hydrocarbons) as vapour. This process is termed as flash evaporation.

Pressure in the flash drum is generally less than 5 bars and requires a typical holdup time of 15-30 minutes. After leaving the flash drum the rich glycol is heated in a heat exchanger to replace the heat lost during the flash process and ensure that it has the same temperature as the stripper before entering it

1.2.2.3 Glycol Regeneration Unit

The glycol regeneration unit is composed of a re-boiler where steam is generated from the water in the glycol. The steam is circulated through the packed section to strip the water from glycol. Stripped water and any lost hydrocarbons are vented at the top of the stripping column. The hydrocarbon losses are usually benzene, toluene, xylene, and ethyl benzene (BTXE) and it is important to minimize these emissions. The rich glycol is preheated in heat exchangers, using the hot lean glycol, before it enters the still column of the glycol re-boiler. This cools down the lean glycol to the desired temperature and saves the energy required for heating the rich glycol in the reboiler.

1.2.2.4 Reboiler

At the bottom, a reboiler is installed. This acts like a heat exchanger and provides the heat required to separate the glycol from water in the stripper. The temperature is mostly based on the degradation temperature of the glycol type being used. For TEG the recommended maximum temperature is 206°C. Steam is used as the heating medium and exits as condensate (water). The lean glycol is taken from the reboiler and recycled back into the absorber. Before it enters the absorber, the lean glycol goes through a heat

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exchanger and a pump to ensure that the temperature and pressures are equal or close to that in the absorber.

1.2.2.5 Condenser

After the vapour leaves the still column, it is routed through a cooling water condenser, which condenses the glycol vapour.

1.2.2.6 Reflux Drum

The reflux drum acts as a distribution point and stores the condensed glycol allowing water vapour to exit. It is mostly used to ensure that the condensed glycol enters the stripper under controlled standards thus ensuring that the right amount of glycol is returned back into the Stripper with the help of control devices. It is also equipped with a pump to manage flow rates.

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GLYCOL DEHYDRATION SYSTEMS

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SAFETY ISSUES AND CHALLENGES

BTEX Emission

TEG Dehydration Systems emit several billion cubic feet of toxins annually. Emissions include hazardous air pollutants (HAP’s), volatile organic compounds (VOC’s) which are highly flammable, and BTEX which consists of benzene, toluene, ethyl benzene and xylenes, which are lethal carcinogens (cause cancer to human).

Benzene, toluene, ethyl benzene and xylene (BTEX) is a problem because of environmental concerns. BTEX is removed from the gas during glycol dehydration, a smaller amount BTEX may also be removed during gas sweetening. When the glycol is regenerated the BTEX will be removed with the water, and thereby be vented to the atmosphere. BTEX are also a problem in cryogenic gas treatment because they can freeze like water. BTEX cannot be removed from the gas before the dehydration.

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CHAPTER 3

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SAFETY AND HEALTH MANAGEMENT

Introduction

This section describes overall concept and risk assessment of the TEG Dehydration Systems.

A risk is the potential for a hazard to cause a specified harm to someone or something, i.e. it is a product of both the magnitude (scale of consequences) and the likelihood (frequency) of it occurring. Therefore, to identify the risks associated with a TEG Dehydration Systems, the assessment process needs to identify systematically the hazards, causes and consequences, which may occur or arise from the operation of TEG Dehydration System.

In compliance with normal practice, the level of acceptability for each particular risk is the ALARP level, where ALARP is the level below which the costs to reduce the risk even lower (in terms of both time and effort as well as money) would be greatly disproportionate to the reduction in the risk that could be achieved. Typically, the relationship between the ALARP risk acceptability level, and the frequency and consequence

magnitude

of

a

hazardous

incident

occurring

is

illustrated

diagrammatically in Figure 3.1-1 below.

3.2

Risk Assessment Management Process

The processes of risk assessment management process are as following steps:-

Step 1 – Identify Hazards; Step 2 – Assess Risks; and Step 3 – Specify Risk Control Options.

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Figure 3.1-2 illustrates the risk management process. It comprises a considered, systematic risk planning, identification, analysis, evaluation and treatment/ mitigation process that is supported by appropriate monitoring, review and recording of the identified risks.

C5

E C4 C N E U QC3 E S N O CC2

C1

Catastrophic

INTOLERABLE

Major

A L A R P

Moderate

Minor

ACCEPTABLE

Insignificant

Rare

Unlikely

Possible

Likely

Frequent

F1

F2

F3

F4

F5

FREQUENCY Figure 3.1-1: The ALARP Risk Acceptability Level and its Relationship to the Frequency and Consequence Magnitude of a Hazardous Incident Occurring

3.2.1

Hazards Identification

Hazards identification is a process of determining the area of concerns that are present and relevant which could induce risks. The aim is to identify where, when, why and how events could prevent, degrade or delay the achievement of objectives with the focus on the 'overall picture'.

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Risk Analysis

Risk analysis is a process of measuring the relative level of risk exposure that the identified hazards pose. The level of risk exposure is considered as a product of the likelihood of the risk event occurring and the consequence should it occur.

Figure 3.2-1: Risk Management Process 3.2.2.1 Consequence

The severity of the identified hazards is assessed against the consequence definitions that are specific to the potential impacts as presented in Table 3.2-1.

3.2.2.2 Frequency

The likelihood of the identified hazards is assessed against the frequency definition as listed in Table 3.2-2.

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Table 3.2-1: Frequency Ranking

3.2.2.3 Risk Ranking

Risk ranking is a simplistic technique for an initial sorting of identified area of concerns into categories according to their perceived level of seriousness, to allow them to receive the appropriate level of attention. Risk is defined as the seriousness of an initiating event and is the product of the frequency of occurrence of a scenario and the severity of its consequences. The risk matrix presented in Table 3.2-3.

Table 3.2-3: Risk Ranking

The following risk rating criteria was adopted for the assessment: •

Low risk: 1 – 6, Risk is acceptable and can be managed by routine procedures; however, specific application of resources may not be required.

•

Medium risk: 8 – 10, Risk is acceptable on condition and on-going monitoring or routine procedures have to be in place to ensure level of risk does not increase.

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High risk: 12 – 25, Risk is unacceptable and senior management attention is required; action plans must be developed with clear assignment of individual responsibilities and timeframes to mitigate risk.

3.2.3

Risk Mitigating / Risk Control

Selection of preferred risk mitigations is typically a cost-benefit decision, with preference given to treatments that provide the best all round benefit to or create opportunity for the development. For any particular risk, a number of mitigating measures may be considered, and applied either individually or in combination. The additional mitigation measures will be implemented by the responsible party to reduce the risk to the ‘As Low As Reasonably Practicable’ (ALARP) level.

The risk factors must be identified and respective initiating events, consequences, existing control and mitigation measures as well as need to implement additional mitigation measures. Table 3.2-2 shows the risk mitigation/ risk control pyramid.

Figure 3.2-2: Risk Control Pyramid

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Glycol Dehydration Systems Risk Assessment

The hazards and risk assessment of Glycol Dehydration Systems are explained in Paragraph 3.3.1 and Table 3.3-1 below.

3.3.1

Identified Hazards

3.3.1.1 Toxic Gasses Release to Atmosphere

Toxic gasses of Hazardous Air Pollutants (HAPs), Volatile Organic Compound (VOC) and Benzene, Toluene, Ethyl-benzene and Xylene (BTEX) are gasses that released to the atmosphere during process of regeneration of TEG.

This happens due to the process of absorption that taking place in the TEG absorption column (Contractor) by TEG desiccant. During the process, wet methane gas is supplied at bottom of the column while TEG liquid at top of the column, the process of absorption occur when wet gasses and TEG is contacted inside the column.

The TEG act as an absorber to water vapour in the wet gas, however, other impurities such as HAPs, VOC and BTEX are also absorbed by TEG liquid. These gasses are to be harmful to human if inhaled and BTEX could be carcinogen (cause cancer).

In operation, all of these gasses are flowed to the flare and burned (converting to less hazardous gas i.e. carbon monoxide, carbon dioxide) before releasing to the atmosphere. Toxic gasses release to atmosphere is considered due to leaking.

3.3.1.2 Contacted with TEG

The effects of TEG when physically contacted to human are tabulated in Table 3.3-1 below.

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Table 3.3-1: Effect of TEG when Contacted Human Part / Category Inhalation

Description Short term harmful effects are not expected from vapour generated at ambient temperatures.

Eye

Splashing in eye causes irritation with transitory disturbances of corneal epithelium. Vapours are not irritating.

Skin

Prolonged exposure may cause skin irritation. Abdominal discomfort, nausea and vomiting may occur.

Ingestion

3.3.1.3 Fire or Explosion Due to Ignition of TEG

TEG is colourless, low volatility and water-soluble liquid that mostly used in dehydrator for natural gas. Due to it volatile characteristic, TEG can be a fire hazard o

when exposed to extreme temperature of 176 C (TEG Flash Point) and auto-ignition o

at temperature of 371 C.

3.3.1.4 TEG Spill / Leak

TED spill / leak are considered as a safety hazard to human.

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MITIGATION AND RECOMMENDATION

The risk assessment of Glycol Dehydration Systems is summarised in Chapter 3. The risk results that assessed of moderate to high risk must be controlled and reduced to As Low As Reasonably Practicable (ALARP).

4.1

Mitigation and Recommendation

While Glycol Dehydration Systems has been assessed without high risk of identified hazard, safety precaution or preventive action shall be formulated for all identified hazards. Therefore, the following recommendations have been raised to ensure the risk of Glycol dehydration System is kept at a minimum.

4.1.1

Toxic Gasses Releasing to Atmosphere

Toxic gasses of HAPs, VOC and BTEX must be engineered control by burning its (flare) to become less hazardous gas i.e. carbon monoxide and carbon dioxide.

4.1.2

Fire or Explosion Due to Ignition of Glycol

All sources of ignition must be identified and controlled. No any activity is permitted within the hazardous zone of Glycol Dehydration Systems without concern permission by the authority.

4.1.3

Develop Safe Work Procedure (SWP) and Emergency Response Plan (ERP)

A comprehensive SWP and ERP must be established for Glycol Dehydration Systems.

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CASE STUDY

5.1

TEG Fire at Gas Dehydration Unit

5.1.1

Incident Information

Country Location Incident date Type of Activity Type of Injury 5.1.2

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Spain Onshore 15 May 2013 Maintenance, inspection and testing Explosions or burns

Incident Detail

After a TEG (Triethylene glycol) low level alarm at the natural gas dehydration unit, the unit was stopped and the operator waited 2 hours before opening the TEG inlet. A fire occurred when the TEG vapours, coming from inside the accumulator tank, reached the exhaust stack during the TEG refilling operation. The burner zone has restrictions for operator escape, although on this occasion the operator reached the TEG inlet cap from outside the zone and was not caught by the fire. The fire detector produced a level 1 emergency shut down and the fire was put out by the internal fire brigade without significant consequences (see Figure 5.1-1 ).

5.1.3

Incident Root Cause •

TEG inlet aiming to a hot spot is considered to be an error in design, causing that TEG vapour is directed to a hot spot when the inlet cap in opened.

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Deficient inspection and maintenance plan: the periodic inspection of exhaust pipe for burners was not included in plan.

5.1.4

Corrective Action and Recommendation

•

The TEG inlet must be checked/ modified to ensure that vapours are evacuated to a safe place.

•

A technical instruction shall be prepared to describe TEG refilling operation.

•

Include the inspection of exhaust pipe for all the units with burner in the inspection and maintenance plan.

Figure 5.1-1: Site Incident Photo

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REFERENCES

1.

Abdel-aal H.K., Aggout, M. and Fahim, M.A., 2003. Petroleum and Gas Field Processing. Marcel Dekker, Inc. Dharan, Saudi Arabia.

2.

Christensen, D. L. 2009. Thermodynamic Simulation of the Water/ Glycol Mixture. Aalbog University. Denmark.

3.

Hansen, P., Chiriac, A., Incoom, N. and Olsen, A. 2013. Design of TEG Dehydration Train Model Using the Glycol Property Package in HYSYS . Aalbog University. Denmark.

4.

Moore, Jr., 1999. Glycol Refining (Patent No. 5,882,486). United States Patent, USA.

5.

National Research and Development, Research Triangle Park. 1996. Methane Emission from Natural Gas, Volume 14: Glycol Dehydrator. United States Environmental Protection Agency.

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SAFETY, ENVIRONMENTAL IMPACT & RISK MANAGEMENT

Glycol Dehydration Systems

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